This invention relates generally to spacecraft docking and, in particular, to a system of the type wherein all active components are disposed on a chase vehicle.
There is interest in commercial uses of outer space, particularly earth orbit. This environment offers unique characteristics, such as zero gravity and unlimited vacuum, which may be useful to certain manufacturing processes. A major problem is the costs in launch and recovery of payloads.
One possible solution involves the use of a semi-permanent orbiting vehicle that is periodically serviced for refueling, resupply, and payload exchange. The most economical approach to such operations involves unmanned, unsupervised, autonomous rendezvous and docking vehicles. This requires capture and docking mechanisms which are simple and reliable, even in the presence of some misalignment. It would also be advantageous for the mechanism aboard the normally orbiting craft to be largely passive, thereby preserving power resources for other, perhaps more critical uses.
Existing spacecraft coupling structures typically take the form of compatible male and female devices, such as a conical seating platform on one vehicle and a docking adapter on the other for alignment and coupling of the spacecraft. Such structures typically absorb the relative kinetic energy between the two space vehicles upon engagement, and upon coupling, rigidly and securely interconnect the two spacecraft until their desired disengagement or decoupling.
In most applications, attachment is accomplished by remotely controlling one spacecraft on earth. The controlled vehicle typically includes an elongate probe or grappling arm for insertion into the conical seating platform in the other vehicle. U.S. Pat. Nos. 5,735,488; 5,364,046; 4,177,964; 4,195,804; 4,391,423; and 4,588,150, and Japanese Patent No. 226,497 are illustrative of such structures.
The apparatus described in U.S. Pat. No. 5,735,488 includes an elongate grappling arm extending from a first space vehicle. A pair of inflatable bladders are positioned about the grappling arm for engaging an inner surface of the combustion chamber of a second vehicle upon inflation, and a pair of rear bladders are positioned about the grappling arm for engaging an inner surface of the nozzle downstream from the combustion chamber upon inflation. This aligns the grappling arm and the rocket propulsion nozzle. A pressurized fluid source is provided on the first space vehicle for supplying fluid pressure to the inflatable bladders, and a fluid control valve manifold selectively controls the release of pressurized fluid to the bladders. In operation, the grappling arm is inserted into the rocket propulsion nozzle, and the control valves are actuated to first inflate the front bladders and thereby interconnect the grappling arm and the rocket propulsion nozzle. The rear bladders are subsequently inflated to align a central axis of the grappling arm with a central axis of the rocket propulsion nozzle. Inflation of the rear bladders provides an axial reaction load to balance the axial load provided by the front bladders. Attaching the vehicles in space may be controlled from the earth by activating the control valves to inflate the bladders.
According to U.S. Pat. No. 5,364,046, a largely passive capture mechanism disposed on a first spacecraft includes a concave cone section with the narrower interior end to admit a ball of a predetermined diameter. When tripped, a capture device restricts the diameter of passage for capture of the ball. In the release position passage for the ball is unrestricted. The capture device is preferably reset by the other spacecraft to release the ball. A docking mechanism disposed on the second spacecraft includes a convex cone section constructed to mate with the concave cone section, ball at the end of a cable and a boom. The cable may be extended from or retracted to the apex of the convex cone section. A rotary drive coupled to the convex cone section permits relative rotation of the spacecraft. The boom may be extended from or retracted into the second spacecraft. The spacecraft dock by directing the extended ball into the cylinder, where it is captured. The cable and boom retract to dock. The active docking mechanism releases and resets the capture device to undock. A pyrotechnic cutter disposed inside the boom can cut the cable for emergency release.
This invention solves problems associated with prior-art soft-dock mechanisms by placing all active components of a soft-dock system on the chaser side of the mechanism, leaving the target side of the mechanism completely passive (i.e., requiring no power expenditure or self-actuated moving parts to operate). In particular, the active components are supported on the end of a flexible cable attached to the probe, or chaser, side of the device. These components act as a sort of spring-loaded xe2x80x9ctrap.xe2x80x9d Once the end of the probe passes into a receptacle on the target side, the mechanism is triggered, engaging it in such a way that it can no longer be pulled out of the receptacle until it is reset.